1. Field
The present disclosure relates generally to indoor position or location estimations of mobile communication devices and, more particularly, to techniques for utilizing a reference signal to facilitate or support indoor positioning for use in or with mobile communication devices.
2. Information
Mobile communication devices, such as, for example, cellular telephones, portable navigation units, smartphones, tablets, laptop computers, personal digital assistants, or the like are becoming more common every day. Certain mobile communication devices, such as, for example, location-aware cellular telephones, smart telephones, or the like may assist users in estimating their geographic locations by making measurements of RF signals transmitted either from fixed beacons such as cellular base stations or WiFi or Bluetooth® Access Points or from orbiting positioning satellites whose orbital trajectories are accurately known. In an outdoor environment, mobile communication devices may obtain an estimate of their geographic location or so-called “position fix” by acquiring and measuring wireless signals from a satellite positioning system (SPS), such as the global positioning system (GPS) or other like Global Navigation Satellite Systems (GNSS) and from cellular base stations. Acquired and measured wireless signals may, for example, be processed by a mobile communication device or by a separate location server to determine a location estimate for the mobile device using one or more techniques such as trilateration and pattern matching.
In an indoor environment, certain mobile communication devices may be unable to reliably acquire or accurately measure wireless signals from a sufficient number of satellites and cellular base stations to enable determination of a location estimate or an accurate location estimate. Other techniques may instead be used to enable location or accurate location indoors. For example, a mobile communication device located indoors may obtain a position fix by acquiring and measuring wireless signals from three or more terrestrial wireless transmitters associated with a wireless local area network (WLAN), such as WiFi or Bluetooth access points. The measured access points may be identified in some cases by obtaining a Media Access Control identifier (MAC ID) address from wireless signals received from each access point and one or more characteristics of the received signals may be measured, such as a received signal strength indication (RSSI), round trip signal propagation time (RTT), signal to noise ratio (S/N), signal time of arrival (TOA), or the like. An indoor location for the mobile device may then be estimated using techniques such as trilateration or pattern matching, similar to or the same as techniques used to locate a mobile device outdoors, but applied to measurements of other types of signals. As an example, an indoor location of a mobile communication device may be estimated via radio heat map signature matching, for example, in which current characteristics of wireless signals received from access points at the device (e.g. RSSI, RTT) are compared with expected or previously measured signal characteristics for the access points stored as heat map values in a database.
In some instances, however, such as in larger indoor or like areas (e.g., shopping malls, airports, convention centers, office buildings, etc.), lack of sufficient WLAN transmitters and/or obstacles and impediments to WLAN signal propagation (e.g. imposed by walls in an office building or long distances in an airport or convention center) may reduce the number of WLAN transmitters from which a mobile device can acquire and accurately measure signals, resulting in no location estimate or a very inaccurate location estimate. Methods to improve indoor location in these and other environments may therefore be beneficial.